This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-265326, filed Sep. 20, 1999, the entire contents of which are incorporated by reference.
The present invention relates to a laser scanning microscope for transmitting a laser beam in the ultraviolet (UV) range output from, e.g., a laser source via an optical fiber, and detecting light from a specimen upon scanning it with the laser beam via an objective lens, thereby obtaining an observation image.
Such laser scanning microscopes are used mainly as inspection apparatuses in the industrial field, and are widely used as research observation apparatuses in the medical and biological fields. Inspection apparatuses in the industrial field are strongly required to have increased optical resolving power. The wavelength of a light source is shifting from the visible range to the UV range having a shorter wavelength. In research observation apparatuses in the medical and biological fields, a fluorochrome such as DAPI is used to observe fluorescence from a specimen by irradiating the specimen with a UV light. As the light source, a combination with a UV light is strongly demanded.
In this manner, light in the UV range is being used in the industrial field and the medical and biological fields. In general, the laser source of a UV laser beam is large. Vibrations are generated by a cooling fan and circulation of cooling water, and propagate to a laser scanning microscope main body to adversely influence the main body. Thus, the laser scanning microscope cannot exhibit sufficient stability.
To solve this problem, PCT WO 96/06377 discloses a technique of removing the influence of vibrations and heat generation from a UV laser source by coupling the UV laser source and a microscope main body (containing a scanning device) with an optical fiber.
However, as described in detail in PCT WO 96/06377 as well, when a UV laser beam enters the optical fiber, the exit light quantity from the optical fiber decreases within a short time owing to photochemical reaction, and does not recover.
To prevent this, PCT WO 96/06377 adopts a shutter between a UV laser beam and an optical fiber in order to minimize the decrease in the quantity of exit light from the optical fiber. This shutter allows the UV laser beam to enter the optical fiber only while a specimen is scanned with the UV laser beam or during the image sensing operation.
However, the purpose of the technique disclosed in PCT WO 96/06377 is to prevent an unwanted UV laser beam from entering the optical fiber, and the technique does not fundamentally solve degradation of the optical fiber by photochemical reaction caused by the UV laser beam. If a specimen is kept scanned to sense its image by emitting the UV laser beam toward the optical fiber and transmitting it to the laser scanning microscope, photochemical reaction inevitably proceeds to decrease the exit light quantity from the optical fiber.
It is an object of the present invention to provide a compact laser scanning microscope having stable performance and a high optical resolving power without varying the light quantity of a UV laser beam to a specimen.
According to the first aspect of the present invention, a laser scanning microscope for scanning a specimen with a laser beam having passed through an optical fiber, and obtaining an observation image of the specimen on the basis of light from the specimen comprises a laser source for emitting a laser beam having a first wavelength, an optical fiber for transmitting the laser beam having the first wavelength from the laser source to a microscope main body, and laser modulation means for modulating the laser beam having the first wavelength that has passed through the optical fiber into a laser beam having a second wavelength shorter than the first wavelength.
According to this aspect, the wavelength of a laser beam which passes through the optical fiber can be set longer than that of a laser beam which irradiates a specimen. When, for example, the specimen is to be irradiated with a UV light, the UV light need not pass through the optical fiber. This can prevent a decrease in exit light quantity caused by photochemical reaction in the optical fiber.
According to the second aspect of the present invention, the laser modulation means in the first aspect modulates the first wavelength into a second wavelength serving as a 2nd or higher harmonic.
According to the third aspect, the laser scanning microscope in the first aspect further comprises an optical system for scanning the specimen with at least one of the laser beam having the first wavelength that has passed through the optical fiber, and the laser beam having the second wavelength that is modulated by the laser modulation means.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.